Gas chromatography



Nov. 14, 1961 J. R; ROEHRIG 3,009,661

- GAS CHROMATOGRAPHY Filed July 15, 1958 CARRIER GAS 1 To VENT SAMPLE l INLET 1 l I I l I I T0 VENT I CHROMATOGRAPHY I COLUMN I BALANCED I AMP lFlER I I 201' (5 a; 10 i I I OVEN FIG. I

l, RECORDER KRYPTON 5 F INVENTOR.

Jdkaflxn RaeLr fi l2 Z-HAL/W United States Patent 3,009,061 GAS CHROMATOGRAPHY Jonathan R. Roehrig, Sudbury, Mass., assignor to National Research Corporation, Cambridge, Mass., a corporation of Massachusetts Filed July 15, 1958, Ser. No. 748,658

4 Claims. (Cl. 250-435) This invention relates to the analysis by ionization detectors of gases and is in part a continuation of my copending application, Serial No. 609,033, filed September 10, 1956.

It is an object of this invention to provide a beta particle detector useful in the detection and analysis of high temperature gases.

Another object of this invention is to produce a high signal to noise ratio radioactive ionization detector in a chromatography apparatus which creates a minimum of risk to the health of operating personnel in the event of damage to the apparatus.

A still further object of this invention is to provide a radioactive ionization detector in a chromatography apparatus, the detector having a high signal to noise ratio at high temperature gas conditions which makes possible detection of small concentrations of high temperature sample gases passing from the chromatography apparatus.

Other objects will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangements of parts and the method involving the several steps and the relation and the order of one or more of such steps with respect to each of the others which are exemplified in the following detailed disclosure and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing wherein there is indicated a complete apparatus of this invention including a separation unit, a detector and a recorder of a preferred embodiment.

The objects of this invention are realized by utilizing a radioactive isotope of krypton (Kr 85) as a source of the ionizing particles in an ionization chamber having a special geometry and construction. This chamber cooperates with a unit providing binary combinations of gas such as a chromatographic separation unit and with ion collection and ion current measuring units to yield the desired analysis.

With radioactive ionization detectors, improved accuracy of analysis of sample gases evolved from chromatographic separation depends not only on an accurate determination of the cross-section for ionization of gases in an ion chamber since the dimensions of the ion chamber itself are critical. Each sample gas is evolved over a period of time as carrier gas flows through a chromatographic separation unit. Typically the evolution (ion current) plotted against time follows a curve having a distinct peak between the beginning of evolution of the particular sample gas to the end of evolution of it. To obtain a curve that is closely related to the amount of sample gas eluted from time to time, it is essential that the volume of the ion chamber be small. Peaks for two succeeding gases usually occur at least one second apart. It has been found, under such conditions that the volume of the ion chamber should be no more than the volume of gas to be subject to ionization which flows from the chromatography separation in one second.

For accurate, safe gas analysis, the radioactive source should direct a high intensity of radiation into a limited volume of gas to obtain a good signal-noise ratio and at 3,009,061 Patented Nov. 14, 1961 the same time minimize the size of increment analyzed to obtain high resolution without creating serious health hazards.

Increasing the number of radioactive emanations so as to obtain a good signal-noise ratio requires increasing the amount of radioactive material. For any radio-active material which yields many high energy gamma rays, the mere presence of large amounts of such radioactive material creates a continuing health hazard.

These problems are overcome or circumvented in the chromatography apparatus of this invention by utilizing large amounts of krypton in a gas-tight cylinder through which a thin Walled tube passes. Gases travel from a chromatography separation unit through the tube. Beta particles emanated from the krypton 85 transit the thin-walled tube and ionize the passing gas. An ion collector attached to an appropriate voltage source is located in the chamber defined by the tube and collects ions as they are formed, before any recombination occurs. Suitable electrical circuitry amplifies the ion current.

Where high signal to noise ratio is desirable, the amount of krpton 85 is maintained in such a quantity that at least 0.001 curie and preferably as many as 0.01 curie of beta particles completely traverse the increment of gas flow being analyzed creating enough ions to provide a meaningful ion current for the analysis. The geometry of the ion chamber and beta particle source combination permits such concentrations with small ion chamber vol: umes, permitting high resolutions as well. Moreover, this can be accomplished with subatmospheric concentrations of krypton 85 which obviate the necessity of a difficult compressing step, and which lessens the slight risk of harm that is present if the krypton 85 container develops a leak.

Krytpon 85 is fugacious, hence if its container is damaged the large amounts will escape and will diffuse immediately so that high concentrations will not be present to endanger personnel. Also, krypton 85 is inert. It will not displace body chemicals so that there is no body retention in the event a shock dosage is taken into the body. Thus the only injurious effect of the inhalation of krypton 85 is the period of internal bombardment by its emanations as it makes its rapid transit through the lungs.

Krypton 85 has only a very small amount of gamma radiation (for every curie of beta disintegrations only .007 curie gamma is present) hence the large quantities of krypton required to achieve the objects of this invention can be concentrated in laboratory apparatus without undue personnel hazard from gamma radiations. The nature of the container for krypton 85 makes shielding very easy when it is desired. Thus a container for krypton 85 can be provided with outer walls of lead to provide excellent shielding.

Shielding walls that are sufiicient to protect personnel from gamma radiations also protect the personnel from beta radiations. In addition to the shielding offered by the krypton 85, beneficial shielding is obtained by the walls of an oven used in a preferred embodiment to ob tain high temperature chromatographic separation of gases being analyzed and to obtain steady detecting conditions in the detector itself.

Large quantities of krypton 85 thus can be employed in the apparatus of this invention to obtain a good signal-noise ratio and good resolution with no risk to health either in operation of the detector or in the event of damage to the detector.

A further, very important advantage obtained is that regardless of the temperature of the gases flowing from the chromatography separation unit, the detector operates consistently. Because many chemicals to be analyzed by gas chromatography separation are adequately separable only by increasingtemperature during a separation run,

3 the fact that the high-signal to noise ratio and the high resolution with low hazard to personnel can be obtained in detecting gases having high temperatures is an eX- tremely important advance in chemical analysis.

By utilizing a reference chamber (one through which only the carrier gas flows under the same conditions as it flows through the separation means) which is subjected to the same temperature and is constructed in the same manner as the detecting chamber, and by subtracting the current thus obtained from the current from the detecting chamber, the resulting current is directly related to the amount of sample gas in the detecting chamber at the instant of reading.

Referring now to the drawings the invention of this application will be explained in more detail:

In FIG. 1 there is shown a chromatography column connected to a detector generally indicated at 12. Both the column and the detector are located in a controlled temperature oven 14. A chemical sample to be analyzed is introduced into the column 10 through an inlet 16 and is flushed through this column by carrier gas flowing from a carrier gas supply 18. Ionization current produced in the detector 12 is related to the gas flowing through the detector and is fed to a balanced amplifier 20 connected to a recorder 22. This recorder is controlled by the amplified ionization current from the detector 12 and preferably records the relative concentrations of the gases analyzed or the integrated concentrations thereof.

The detector 12 comprises two ionization chambers shown in cross-section in FIG. 2. One ion chamber is defined by tube 30 and the other by tube 32. Tube 34 is connected to column 10 and tube 32 is connected to pipe 34 which is connected directly to the carrier gas supply 18. Suitable valves 50 control the flow of gases through the detector. A substantial portion of pipe 34, comprising that part adjacent to tube '32, is located in the controlled temperature oven 14. Two ion collector electrodes 36 and 38 are provided, one for each ion chamber. Each electrode is connected to a voltage (e.g. 300 v.) which permits the collection of all ions formed in the tube, but is not so great as to cause gas amplification. The electrodes pass into the chambers through insulators 40 (preferably positioned outside of the oven 14 as shown in FIG. 1), the electrodes 36, 38- are connected to the balanced amplifier 20 in such a way that only the difference between the ion currents collected by the two electrodes 36 and 38 is amplified.

Surrounding the tubes 30 and 32 is a gas-tight chamber 42 which defines a space adjacent to each of the tubes filled with krypton 85, at slightly less than atmospheric pressure.

The walls of the tubes 30 and 32 are thin so as to permit the passage of beta particles from the krypton 85 into the ion chambers defined by the tubes. In one preferred embodiment tubes 30- and 32 are of aluminum. In an embodiment preferred for high temperature operation the tubes 30 and 32 are formed of Monel or stainless steel with tubular wall thickness of approximately 2 mils, the tubes each having an inner diameter on the order of A1 to /2 inch. I The surrounding gas-tight chamber 42 is sealed in gas-tight fashion to the tubes 30 and 32 preferably by soldering or in the case of stainless steel and the like, by heliarc welding. The gas-tight chamber is evacuated through a suitable connection (not shown) and then filled withkrypton 85 at a preferred pressure of about 500 mm. Hg abs. Thegas-tight chamber 42 is so constructed that a layer several millimeters thick of krypton 85 is maintained in contact with substantially all of the outer surfaces of tubes 30 and 32. That portion of each tube which is subjected to the krypton 85 radiation is preferably defined by a length which makes the volume contained in each of the tubes equal to the volume of gas flowing through the tube in one second. When high resolution is desirable, the collecting electrodes are so arranged that they collect ions from these limited volumes.

In operation of the device of FIGS. 1 and 2 oven 14 is brought up to a suitable temperature e.g. ZOO-400 C. A carrier gas, e.g. helium, hydrogen or argon is passed through column 10 and pipe 34. The flow is adjusted for instance by manipulation of valves 58, and the ion current produced at each of the collecting electrodes 36 and 38 is balanced so that no indication is obtained by the device. A sample is inserted through inlet 16 into the flowing stream of carrier gas and the sample is eluted from the column 18 by the carrier gas, the constituents of the sample being separated into successive binary combinations with the carrier gas. These pass through tube 30. The difference between the ion currents obtained at electrodes 36 and 38 is amplified by the amplifier 20 and indicated on recorder 22. An analysis of the sample is thus obtained.

The passages formed by tubes 30 and 32 can be formed in many alternative ways. For instance, a large tube can be divided longitudinally by a gas-tight partition into two passages, or the tubes can be provided in a connected relationship like that of the barrels in a double-barreled shotgun.

The preferred embodiment of FIG. 1 indicates an oven. Wherever controlled temperature operation is desired, or where portions of the sample being analyzed have high boiling points are to be analyzed, an oven of the nature described should be utilized. In some uses of the invention such a heating means is not required. It should be noted that in some instances, it may be desirable to include only the detector or only the chromatography column in an oven, or to utilize separate ovens for enclosing each component of the system. All of these alternative embodiments are within the spirit of this invention.

The recorder may be of one of the types illustrated in my copending application, Serial No. 609,073, filed September '10, 1956, or it may be of any of a number of less desirable recorders which provide a permanent plot of ion current versus time.

The krypton may be provided at a variety of pressures, subatmospheric being preferred because of the difficulty in compressing and the danger of leaks.

Since certain changes may be made in the above apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description, or shown in the accompanying drawings, shall be interpreted as illustrative, and not in a limiting sense.

What is claimed is:

1. A gas analysis apparatus comprising a gas chromat0 graphy separation unit, a detector, a detector current recorder and metallic oven means, said oven means surrounding the chromatography unit and detector and providing controlled temperatures up to 400 C. to effect resolution of high boiling point gases, said detector comprising an inner metallic passage for said flow of gases, an outer metallic chamber surrounding at least a portion of said passage in a gas-tight manner, a portion of said inner passage so surrounded being defined by Walls sufliciently thin that beta particles emitted from krypton 85 pass therethrough, said outer chamber being filled with at least some krypton 85, and said detector being further equipped with a means for collecting ions formed in said inner passage by beta particles emitted from said krypton 85 and for causing an electrical current to flow in response to said collected ions and means for measuring said electrical current providing an indication of the concentration of one of the gases of the binary combination in the other.

2. A gas analysis apparatus comprising a ga chroinatography separation unit, a detector, a detector current recorder and oven means, said oven means surrounding the chromatography unit and detector and providing controlled temperatures up to 400 C. to eltect resolution of high boiling point gases, said detector comprising an outer chamber substantially surrounding a pair of thinwalled tubular passages through which gases flow, said tubular walls being sufficiently thin that beta particles emitted from krypton 85 pass therethrough, said outer chamber being gas-tight and so constructed as to provide a space between the walls of said chamber and the inner tubular passages and containing a substantial quantity of krypton 85 in contact with substantially all the outer surfaces of said tubular passages whereby beta particles emanated from said krypton pass through the thin walls of the inner tubular passages and through the gases contained therein, each said tubular passage having contained therein an ion collecting electrode to collect ions of the gas therein which are created by ionizations caused by the beta particles in said inner tubular passage, one of said tubular passages being arranged to receive the binary combinations of the carrier gas and gases to be analyzed which flow from said chromatography column and the other being arranged to receive only the carrier gas.

3. A gas analysis apparatus comprising a gas chromatography separation unit, a detector, a detector current recorder and oven means, said oven means surrounding the chromatography unit and detector and providing controlled temperatures up to 400 C. to effect resolution of high boiling point gases, said detector com-prising an outer chamber substantially surrounding a pair of thin-walled tubular passages through which gases flow, said tubular walls being sufiiciently thin so as to present no more obstruction to the passage of beta particles than does 5 mils of aluminum, said outer gas-tight chamber containing a sutficient quantity of krypton 85 and being so const-ructed that "a depth of krypton 85 of at least 1 mm. is in contact with substantially all the outer surfaces of said tubular passages whereby at least .001 curie of beta particles emanated from said krypton pass through the thin Walls of the inner tubular passages and through the gases contained therein, each said tubular passage having contained therein an ion collecting electrode to collect ions of the gas therein which are created by ionizations caused by the beta particles in said inner tubular passage,

one of said tubular passages being arranged to receive the binary combinations of the carrier gas and gases to be analyzed which flow from said chromatography column and the other being arranged to receive only the carrier gas, each tubular passage being defined by a length which makes the volume contained in each of the tubes no greater than the volume of gas flowing through the tube in one second.

4. A gas analysis apparatus comprising a gas chromato graphy separation unit, a detector, a detector current recorder and oven means, said oven means surrounding the chromatography unit and detector and providing controlled temperatures up to 400 C. to efiect resolution of high boiling point gases, said detector comprising an inner passage for said flow of gases, an outer chamber surrounding at least a portion of said passage in a gastight manner, a portion of said inner passage so surrounded being defined by walls sufliciently thin that beta particles emitted from krypton pass therethrough, said outer chamber being filled with at least some krypton 85, and said detector being further equipped with a means for collecting ions formed in said inner passage by beta particles emitted from said krypton 85 and for causing an electrical current to flow in response to said collected ions and means for measuring said electrical current providing an indication of the concentration of one of the gases of the binary combination in the other.

References Cited in the file of this patent UNITED STATES PATENTS 2,641,710 Pompeo et a1. June 6, 1953 2,755,388 Weisz July 17, 1956 2,761,976 Obennaier et a1. Sept. 4, 1956 2,884,538 Swift Apr. 28, 1959 FOREIGN PATENTS 737,386 Great Britain Sept. 28, 1955 OTHER REFERENCES A Comparison of Detection Methods for Gas Chromatog-raphy Including Detection by Beta Ray Ionization, article by H. Boer, in Vapor Phase Chromatography, pages 169-184; presented at the London Symposium on June 1, 1956. 

